Amazon.com said it's buying The Book Depository International, an online bookseller and publisher based in the U.K., for an undisclosed price.

The 7-year-old British site, which focuses on less mainstream titles, has more than 6 million titles in its inventory, and is considered to be one of Amazon's main competitors in the U.K. The Book Depository also republishes books that are no longer available through its Dodo Press printing department.

"Customers in more than 100 countries enjoy The Book Depository's vast selection, convenient delivery and free shipping," said Greg Greeley, Amazon's Vice President of European Retail in a statement. "The Book Depository is very focused on serving its customers around the world, and we look forward to welcoming them to the Amazon family."

It's not yet clear how Amazon will integrate The Book Depository into its e-book and publishing business, though, via Twitter, the British company said it will continue to operate independently. Amazon already has dedicated Kindle stores in the U.K. and Germany, as well as sites in France, Japan, Canada, China and Italy.